In a third generation (3G) mobile communication system, a service centralization and continuity (SCC) application server may provide various services including IP multimedia subsystem (IMS) centralized services and IMS service continuity. Particularly, the SCC application server may provide a domain selection function and a domain transfer function to a user equipment connected to a typical circuit switched (CS) domain through a mobile access network, such as a universal terrestrial radio access network (UTRAN), a GSM/EDGE radio access network (GERAN), or an IMS network.
The domain selection function may enable a user equipment to select a domain in order to be connected with a call through an IMS domain. The domain transfer function may enable a user equipment to transfer a connected call from a CS domain to a packet switched (PS) or vice versa according to given conditions. Such functions of the SCC application server may extend a wireless service coverage area. In particular, the functions of the SCC application server may transfer a certain call to a wireless network such as an IM core network subsystem. Accordingly, the SCC application server may reduce the load of mobile communication networks.
In order to provide such services of the SCC application server, the SCC application server needs to have information on all networks that a subscriber is registered to. However, related SCC technical standards do not define location registration in existing networks such as a wideband code division multiple access (WCDMA) network. For example, a user equipment in a WCDMA network does not register its location at an SCC application server, so backward compatibility to the WCDMA network is not supported. Accordingly, a fixed mobile convergence (FMC) seamless service cannot be provided to a user equipment using a WCDMA network.